1. Field of the Invention
The present invention relates to a car navigation system and more particular, to a technique of processing traffic information such as traffic jam or travel time and a technique of receiving and outputting processed traffic information in a system for performing communication between a car terminal and a server.
2. Description of the Related Art
There are disclosed systems in which when start and end points are transmitted from a car terminal to a server, the server searches for a route, searches for traffic information, and then returning both of the route and the traffic information to the terminal, in JP-A-2001-356021 and JP-A-2001-289656. In these systems, all the traffic information existing on the route are searched for and returned to the terminal.
Such a technique for estimating a travel time based on other information with respect to a link having no information about travel time as traffic information (which will be referred to as non-provision link, hereinafter) as disclosed in JP-A-7-129893, is known. In the technique, the average vehicle speed of the link is calculated based on traffic jam or congestion information included in external information. And the complementary information for the non-provision link is calculated based on the calculated average vehicle speed. The travel time of the link is also estimated based on the average vehicle speeds of individual time zones for each of previously stored links.
Such a technique for finding a reliability in the predicted value of the run time as disclosed in JP-A-2002-260142, is known. In the technique, data about run times of a road section including the road in question until the current time are collected, a run time memory table having run time data past collected is searched for one of patterns similar in the run time, and a run time memory value for the pattern is used as a predicted run time ahead of N hours. By repeating such operations, a plurality of candidates of the predicted run time are found, most frequent one of the candidates is determined as the predicted run time, and the reliability of the predicted run time is found on the basis of a spread in the distribution of the candidates.
The technique disclosed in JP-A-7-129893 is intended to be applied to a vehicle route guiding system. However, traffic information is updated from moment to moment, and when traffic information past received are also included in the first-mentioned traffic information, a memory capacity and a processing quantity correspondingly become enormous. In such a vehicle route guiding system as not enough in the memory capacity and processing performance, generally speaking, it is difficult for the system to estimate a travel time of a non-provision link on a real time basis. In addition, it is also inefficient for individual vehicle route guiding systems to perform the same operations.
The technique disclosed in JP-A-2002-260142 has a problem from a viewpoint of convenience. For example, even when a prediction error Ws within a probability S is found, the error Ws may fail to fall in a practical range. For example, the prediction error Ws within 90% of a probability S for a predicted run time value of 20 minutes becomes 100 minutes or so.